US2015/0153212 discloses a method of measuring a height of a fuel surface of fuel in an aircraft fuel tank. One or more images of the fuel surface are captured, each image including a fuel surface line where the fuel surface meets a structure. Each image is analysed in order to determine a height of the fuel surface line at three or more points in the image. If the fuel surface line is not a straight line, then an average angle of the fuel surface line can be determined from the points in the image by spatial averaging. Preferably a series of images of the fuel surface are captured over a time period, and an average height of the fuel surface is determined from the series of images by time averaging. The height of the fuel surface line(s) at three or more points is used to determine a volume of the fuel, a mass of the fuel, and/or an attitude of the fuel surface.
A Time-of-Flight Camera (ToF Camera) is a range imaging camera system that resolves distance based on the known speed of light. A ToF Camera is based on the laser rangefinder principle: a very short laser pulse is sent against a target and the time-of-flight (i.e. the time the laser pulse takes to be reflected and to come back to the receiver) is measured. Knowing the speed of propagation of the light the distance can be resolved.
A ToF Camera is a 3D version of a laser rangefinder, where the receiver is a matrix of pixels, and each pixel is able to measure the time-of-flight for the emitted light/laser pulse reflected by a specific region of a 3D object. The final result is a 3D map (or distance map) of the real 3D object. There are typically no moving parts within the ToF Camera and a 3D map of an object can be done in a single measurement. Acquisition rates of 50-60 Hz have been achieved with commercial systems.
A 3-D imaging system is described in WO2006/097406. A photodiode or sensor cell are placed in an illumination unit. The sensor cell provides a phase reference essentially corresponding to a zero distance measurement.